The robotic arm on the Mars Lander found itself in a tough position over the weekend.

After receiving instructions for a movement that would have damaged its wrist, the robotic arm recognized the problem, tried to rectify it and then shut down before it could damage itself, according to Ray Arvidson, a co-investigator for the Mars Lander's robotic arm team and a professor at Washington University in St. Louis.

NASA engineers yesterday worked to send new instructions to the Lander so the robotic arm would come back to life and proceed with a new task. The team is now waiting to see whether the code resolved the problem.

The shutdown led to another delay hampering the long string of experiments that the Mars Lander is slated to conduct on the northern pole of Mars. The Lander had a three-month window to analyze the area before the temperatures drop too low for the equipment to function. Half of that window has closed, and there are still plenty of experiments left to run, officials note.

"I think there's a sense that we should have delivered more materials to analysis," said Arvidson, noting that mission is on Sol 49, or the 49th Martian day. "We're anxious that Sol 90 will be here before you know it. We'll get more effective as we see what the show-stoppers are. It takes patience and time to get all the work done."

The show-stopper this past weekend came in the form of an errant instruction from Earth. Arvidson explained that the robotic arm had been working with an instrument that basically is an electric fork that gauges thermal and electric conductivity in the Martian soil. The arm had stuck the fork in the ground to run analysis. Over the weekend, scientists sent the robotic arm instructions to pull the fork out of the ground and keep it vertical while moving it to the side and shaking any excess soil off of it.

However, the movement was forcing the robotic arm to twist its wrist too far. The robot realized that it was about to damage itself so it moved the other way and then realized that it no longer had the proper coordinates for what to do next, so it left the fork sticking up in the air, stuck its scoop in the ground and stalled itself.

"It was smart enough to know not to do that," said Arvidson. "The system operated exactly as it was supposed to. That was pretty neat."

On Monday, NASA programmers sent new code up to the Lander to re-engage the arm and move on to the next experiment, which will be to use the rasp to shave off ice particles and move them into an oven to be analyzed.

For the past several weeks, NASA scientist have been running a series of tests on the oven instruments -- dubbed TEGA -- to determine why a short-circuit occurred during the instrument's first, and only, test.

The Lander's eight analysis ovens heat Martian soil so that any gases emitted can be analyzed. On that first test, which was done in mid-June, one of the ovens short-circuited. NASA scientists stalled any further TEGA analysis to study the problem. The study concluded that the problem occurred when they had to vibrate the oven far beyond what it was designed to take to get the clumpy Martian soil down into it.

He added that they hope there won't be any further short-circuits. But just in case, they have moved a critical ice test up to the front of the line.

Arvidson said they will take two or three Sols to widen a trench, and then they will take one or two test runs on scraping off ice shavings and moving them quickly into the oven. If they don't move quickly enough, the ice could evaporate before it reaches the test instrument.

Scientists are hoping to run the TEGA test on the ice sample by the end of the week.